Printing devices such as computer printers, photocopiers, etc. which place information onto one or more print media are well established. Less established are devices which print an erasable image onto a print medium. Various marking formulations have been used which provide an image which can be easily erased, requiring an exposure to heat and visible light for a period of less than 10 seconds to effect a complete image erasure. However, these formulations have the drawback of fading over a period of three days or so when exposed to ambient light. Other erasable image marking formulations print a more permanent image and have a lifetime of weeks to months, but have the drawback of being difficult to erase, requiring about two minutes for complete erasure, which is generally considered excessively long for most uses.
An inkless erasable imaging formulation is the subject of U.S. patent application Ser. No. 12/206,136 filed Sep. 8, 2008 and titled “Inkless Reimageable Printing Paper and Method” which is commonly assigned with the present application to Xerox Corp., and is incorporated in its entirety herein by reference. An embodiment of the chemical formulation detailed in the co-pending application comprises a photochromic material, for example an alkoxy modified dithienylethene. Use of this material allows for the imaging of a pattern onto the medium using patterned ultraviolet (UV) light. In use, the print medium is coated with the chemical formulation which is then cured and exposed to a patterned UV light source, such as from a light emitting diode (LED). The UV light chemically alters the formulation to produce a visible image pattern. The image is reasonably stable and remains visible for a longer period of time when exposed to ambient light than conventional erasable inks, for example weeks to months, but is erasable on demand using one or more of visible light and heat. The chemical formulation is reprintable such that the same or a different pattern can be printed using a UV light pattern. The formulation comprises the use of an infrared-absorbing dye additive which heats faster than conventional dyes and thus effects complete erasure in a shorter period of time.
With the advent of a rewritable printing formulation which overcomes the competing problems of image longevity versus erasure difficulty found with conventional erasable image printing processes, other problems related to printing and erasing the chemical formulation onto a print medium can be addressed.